Lubricating compositions generally comprise a base oil of lubricating viscosity together with one or more additives to deliver properties including for example, reduced friction and wear, improved viscosity index, detergency, and resistance to oxidation and corrosion. A lubricant base oil may comprise one or more sources of lubricating oil, referred to as base stocks.
Lubricant base stocks used in automotive engine lubricants are generally obtained from petrochemical sources, for example as the higher boiling fractions isolated during the refining of crude oil or as the products of chemical reactions of feedstocks from petrochemical sources. Lubricant base stocks can also be made from Fischer-Tropsch wax.
Lubricant base stocks may be classified as Group I, II, III, IV and V base stocks according to API standard 1509, “ENGINE OIL LICENSING AND CERTIFICATION SYSTEM”, September 2012 version 17th edition Appendix E, as set out in Table 1.
TABLE 1SaturatedSulphur contenthydrocarbon(% by weight)ViscositycontentASTM D2622Index(% by weight)or D4294 orASTMGroupASTM D2007D4927 or D3120D2270I<90and/>0.03and≥80 andor<120II≥90and≤0.03and≥80 and<120III≥90and≤0.03and≥120IVpolyalphaolefinsVall base stocks not in Groups I, II, III or IV
Group I, Group II and Group III base stocks are generally derived from mineral oils. Group I base stocks are typically manufactured by known processes comprising solvent extraction and solvent dewaxing, or solvent extraction and catalytic dewaxing. Group II and Group III base stocks are typically manufactured by known processes comprising catalytic hydrogenation and/or catalytic hydrocracking, and catalytic hydroisomerisation. Group IV base stocks include for example, hydrogenated oligomers of alpha olefins. Suitable processes for the preparation of the oligomers include for example, free radical processes, Zeigler catalysed processes and cationic Friedel-Crafts catalysed processes. Suitably, polyalphaolefin base stocks are derived for example from C8, C10, C12, C14 olefins and mixtures of one or more thereof.
In recent years, there has been an increased focus on identifying sustainable replacements for products that have historically been obtained from fossil sources. Bio-derived materials (sometimes also called biobased materials) can play an important role in future lubricant formulations, both in meeting customer demand for “green” products and in reducing dependence on non-renewable resources for example crude oil.
Lubricant base stocks have been obtained from vegetable sources, generally as triglyceride esters of fatty acids, such as palm oil, sunflower oil and rapeseed oil. Free fatty acids from vegetable and animal sources may also be used in the preparation of various synthetic ester base stocks.
US2007/0281873 relates to a lubricating oil composition for fluid dynamic bearings which comprises 50 to 100% by mass of an ether compound comprising at least one ether bond and having 11 to 34 carbon atoms as a base oil and has a kinematic viscosity of at least 2.2 mm2/s at 100° C.
The use of six percent of lithium stearate in dihydrocitronellyl ether to form a grease is described by Pethrick S A and Wood H S in “Greases for Use over the Temperature Range −65° C. to +100° C.” Selected Government Research Reports (Great Britain Ministry of Supply), Lubricants and Lubrication (1952), Volume 11 Report. No. 2, 11-20. On page 16 of the Report it is stated:
“In research work on synthetic hydraulic oils, workers in the Faraday Laboratory of the Royal Institution discovered that dihydrocitronellyl ether has a low freezing point combined with low viscosity. A pint sample of this material was made by a manufacturer and a few preliminary experiments were made on the utility of this ether for grease making. Six percent of lithium stearate in the ether formed a grease which when applied to a bearing allowed the latter to be rotated with ease at −70° C. Some bleeding occurred with this grease on storage for two months, but it is anticipated that this could be obviated by compounding with aluminium stearate in addition to the lithium stearate. The volatility of this ether is approximately the same as that of oil to specification D.T.D.44D when tested by I.P. method 46/42, so that no trouble due to evaporation would be expected from a grease made from this material.”
A dihydrocitronellyl moiety contains two isoprenyl units.
Benemann, J. R. et. Al. in “Chemicals From Salt Loving (Halophilic) Microbes” Final Report, National Science Foundation NSF/CPE-82006 May 1982 states in its abstract: “The possibility of producing specialty chemicals—specifically diphytanyl glycerol ether (DPGE), a potential lubricating agent, was examined . . . ”. In the conclusion it is stated: “The results obtained during this investigation do not support the premise that lipids from Halobacteria can be economically produced. The yields obtained were very low under all conditions tested; recoveries for DPGE were even lower than those reported in the literature . . . . Glycerol ethers, if useful as specialty lubricants would be more easily synthesized chemically.”
There remains a need in the art to identify new renewable sources of lubricant base stocks. In particular, there remains a need in the art for high performance lubricating oil compositions which contain base stock which may be bio-derived (also called biobased), at least in part.